Diclofenac sodium exerts excellent antipyretic, analgesic, and anti-inflammatory effects. Drug preparations containing diclofenac sodium are generally divided into peroral drugs exhibiting a systemic action and drugs for external use exhibiting a topical action. When a peroral drug is administered, grave, systemic adverse effects such as gastrointestinal disorders occur, thereby calling for further development of percutaneous-absorption-type patches for topical application for mitigating such adverse effects. In connection with a patch containing a non-steroidal analgesic anti-inflammatory drug such as diclofenac sodium, the most important issues are effective, sustained percutaneous absorption of the active ingredient into the disturbed portion directly under the patch and delivery of the active ingredient to the disturbed portion directly under the patch.
Since diclofenac sodium has considerably low solubility in water and an oily component, a wide range of studies have been carried out in order to stabilize it in a dissolved state in a drug for external use for promoting percutaneous absorption from a patch. For example, Japanese Patent Application Laid-Open (kokai) No. 61-280426 discloses incorporation of an organic acid (citric acid) as an additive for enhancing the solubility and percutaneous absorbability of diclofenac sodium. Japanese Patent Application Laid-Open (kokai) No. 4-193826 discloses incorporation of an essential oil component such as menthol or mentha oil as a percutaneous absorption promoter for diclofenac sodium. Japanese Patent Application Laid-Open (kokai) No. 5-178763 discloses incorporation of a polyhydric alcohol medium-chain fatty acid ester as a solubilizer for slightly soluble drugs. Japanese Patent Application Laid-Open (kokai) No. 11-222443 discloses incorporation of 1-menthol and a pyrrolidone (pyrrolidone or at least one derivative thereof) as a percutaneous absorption promoter for diclofenac sodium.
However, percutaneous absorbability of a drug containing diclofenac sodium for external use is still unsatisfactory, and thus, there still remains a need for a drug for external use which promises more effective percutaneous absorption.
Thus, an object of the present invention is to provide a patch which exhibits excellent releasability and percutaneous absorbability of diclofenac sodium.